1. Field of the Invention
The present invention relates to a method for producing graphene, and more particularly to the method for producing thin graphene nanoplatelets and thin graphene nanoplatelet precursors.
2. Description of Related Art
Graphene, also known as single-layer graphite, is a planar thin film with a hexagonal honeycomb lattice formed by bonding carbon atoms at the sp2 orbit and a two-dimensional material with a thickness of one carbon atom (approximately 0.34 nm).
At present, graphene is the thinnest and hardest nanomaterial substantially transparent and having a heat conductivity coefficient up to 5300 W/m·K which is higher than that of carbon nanotubes or diamond, and this material is suitable for manufacturing heat conductive materials and thermal boundary materials. At room temperature, the electron mobility of graphene (exceeding 15000 cm2/V·s) is approximately equal to 1.5 times of the electron mobility of a carbon nanotube (approximately 10000 cm2/V·s) and ten times of the electron mobility of a crystalline silicon (approximately 1400 cm2/V·s), and the resistance of graphene is approximately equal to 10−6 Ω·cm which is lower than the resistance of copper and silver, so that graphene is considered as a material with the smallest resistance now. Due to the very low resistance, the electron mobility of graphene is very high, so that graphene is expected to be used for the development of new-generation thinner and more highly conductive electronic devices. Since graphene is a substantially transparent conductor, it is suitable for the manufacture of transparent touch screens, light panels, lithium batteries, super capacitors and solar cells.
In general, graphene is prepared or produced by the following four main methods. (1) Mechanical exfoliation method: Graphene is manufactured from graphite, and this method can produce single-layer or multi-layer graphene simply, easily and quickly, but this method is suitable for the manufacture of a small quantity of graphene only; (2) Chemical vapor deposition method or an epitaxial growth method: Graphene is manufacturing by passing and depositing a thermally cracked hydrocarbon gas source onto a nickel or copper plate. This method has the feature of producing large-area single-layer or multi-layer graphene easily and the difficulty of controlling the uniformity and thickness of the graphene; (3) Method of growing graphene on an insulating substrate: A very thin layer of graphene is grown on a surface of silicon carbide. The method has the drawbacks of incurring a high cost and having difficulties of manufacturing large-area graphene; and (4) Method of using organic acidic solvent to insert layers to produce graphene oxide (GO) and obtaining grapheme by a reduction procedure: This method has the drawbacks of requiring a long processing time, and having an inconsistent quality of the grapheme since the reduced grapheme may be deformed or warped easily.
In the aforementioned techniques, high-purity natural graphite powder or expensive sheet monocrystalline natural graphite is used as the raw material, and a chemical acid intercalation process is provided for producing the graphene, and thus the processing is very long and requires a reduction process before high-quality graphene can be obtained, and mass production of graphene is not easy. Therefore, it is a main subject for related manufacturers to develop a method of producing a thin graphene nanoplatelet precursor with high efficiency and cost-effectiveness and applying the precursor in the manufacture of thin graphene nanoplatelets, while taking the cost and time into consideration for manufacturing the thin graphene nanoplatelets effectively.